Abstract
Under anaerobic/hypoxic conditions, Saccharomyces cerevisiae relies on external lipid supplements to modulate membrane lipid fraction in response to different stresses. Here, transcriptomic responses of two S. cerevisiae wine strains were evaluated during hypoxic fermentation of a synthetic must with/without ergosterol and oleic acid supplementation. In the absence of lipids, the two strains, namely EC1118 and M25, showed different behaviour, with M25 significantly decreasing its fermentation rate from the 72 h after inoculum. At this time point, the whole genome transcriptomic analysis revealed common and strain-specific responses to the lack of lipid supplementation. Common responses included the upregulation of the genes involved in ergosterol biosynthesis, as well as the seripauperin and the heat shock protein multigene families. In addition, the upregulation of the aerobic isoforms of genes involved in mitochondrial electron transport is compatible with the previously observed accumulation of reactive oxygen species in the two strains during growth in absence of lipids. Considering the strain-specific responses, M25 downregulated the transcription of genes involved in glucose transport, methionine biosynthesis and of those encoding mannoproteins required for adaptation to low temperatures and hypoxia. The identification of these pathways, which are presumably involved in yeast resistance to stresses, will assist industrial strain selection.
Highlights
During white wine fermentation, S. cerevisiae is subjected to (i) high osmotic pressure, (ii) limited nitrogen concentrations, (iii) prolonged hypoxic/anaerobic conditions, (iv) the presence of chemical preservatives, (v) increasing ethanol concentrations, and (vi) low temperatures
The same strains strains were inoculated in synthetic juice (SJ) enriched with oleic acid and ergosterol (FSJ)
While EC1118 was able to were inoculated in SJ enriched with oleic acid and ergosterol (FSJ)
Summary
S. cerevisiae is subjected to (i) high osmotic pressure, (ii) limited nitrogen concentrations, (iii) prolonged hypoxic/anaerobic conditions, (iv) the presence of chemical preservatives (sulphites), (v) increasing ethanol concentrations, and (vi) low temperatures. White winemaking represents an interesting process to understand yeast response and adaptation to many different stresses occurring during industrial processes. The Target of Rapamycin (TOR) pathway allows yeast cells to adapt to nitrogen limitation conditions by triggering morphological transitions such as pseudohyphal growth and biofilm formation [2,3]. Reactive oxygen species (ROS) generated during wine fermentation trigger the production of proteins needed to protect the cells against oxidative stress [4,5]. Temperature changes activate the production of heat shock proteins (HSPs) through the Heat Shock Response pathway [6,7]. HSPs, involved in folding, stabilization or degradation of protein aggregates, are controlled by the General Stress
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